0.) There are better and far easier to obtain choices. Searing words, 496 rep agi trinket, darkmoon trinket, etc.
1.) Neither mastery nor dodge adds any dps.
2.) It's an inconsistent trinket. Mastery adds to EH, dodge decreases damage taken. If they were pure EH trinkets, say mastery passive and a proc that healed you when melee brings you below 35%, then they'd be swappable in certain situations. As it is, they caters to no niche.
3.) Mastery isn't a particularly strong stat for us, the general consensus is that crit/exp/hit are all significantly more important.
4.) Dodge is an even less preferable stat for us, especially dodge on a proc.

0.) There are better and far easier to obtain choices. Searing words, 496 rep agi trinket, darkmoon trinket, etc.
1.) Neither mastery nor dodge adds any dps.
2.) It's an inconsistent trinket. Mastery adds to EH, dodge decreases damage taken. If they were pure EH trinkets, say mastery passive and a proc that healed you when melee brings you below 35%, then they'd be swappable in certain situations. As it is, they caters to no niche.
3.) Mastery isn't a particularly strong stat for us, the general consensus is that crit/exp/hit are all significantly more important.
4.) Dodge is an even less preferable stat for us, especially dodge on a proc.

The problem is more that their usefulness varies from encounter to encounter, whereas RPS trinkets are consistently useful for everything.

Once you have enough RPS to keep SD up and use T&C on proc (when relevant) survival trinkets become more appealing. Dodge procs (especially those with long ICDs) have a habit of not being up when you need them. On-use trinkets are much better for that kind of build.

I'm a bit confused, what is the optimal stat priority for guardian druids ? I have read this thread, noxxic and icy-veins and they all have different stat priorities. I'm completely new to guardian druid and I will mainly have him for LFR; so what stat priority do you suggest me ?

from what ivbeen reading it seems that early on the survival setup is better, but later on in hc gear the RPS setup gets better.
makes me wonder about 5.2 i gues the RPS setrup will be better then survival there

I'm a bit confused, what is the optimal stat priority for guardian druids ? I have read this thread, noxxic and icy-veins and they all have different stat priorities. I'm completely new to guardian druid and I will mainly have him for LFR; so what stat priority do you suggest me ?

It depends on how you want to tank as a guardian. I'm highly aware that for some the lack of a clear "stat X> stat Y> stat P" etc., will just cause confusion. The reason there isn't just one stat priority for guardians is because of the multiple avenues guardians can take when it comes to damage mitigation.

1). One method is to stack mastery and dodge. That's what we did last expansion, and it's still effective now; dodge obviously increases how often you outright dodge attacks, and mastery increases our armour, and therefore decreases the amount of damage we get hit for when we get hit. This build has the downside of not providing you with as much rage as you might of otherwise of had and therefore limiting the use of the rage costing abilities we have. The reason it limits the use of rage costing abilities is because it utilises "stats" which do not allow us to specialise in generating rage.

The rage costing abilities we have are: "Savage Defense" (a 50% dodge buff). "Tooth and Claw" which can lead on some fights to providing a 100k absorb on the next attack (it stacks as well, so somtimes a 200k absorb etc.). It's especially useful for things like Dread Thrash when combined with "Savage Defense", offering both dodge often in excess of 65% when combined with our passive dodge, and 100-200k absorbs. Finally, there's "Frenzied Regeneration" which allows us to offer some healing to ourselves. This can be especially useful after a spike in damage.

Going with the passive mastery and dodge build wont see you get as much use out of abilities like "Savage Defense" as you would have if you had gone with a build which actively seeks to get you as much rage as possible. Now getting as much rage as possible involves relying on typical dps (Damage Per Second) stats, though the amount of rage you generate isn't necessarily linked to the amount of dps you do.

2). This is the second method. Here one stacks "rps" (rage per second) stats, which attempts to get us as much rage as is reasonably possible so that one can use the above abilities like "Savage Defense" as much as is reasonably possible. The idea here is that providing one can get enough rage one can have a very high "up time" on abilities like "Savage Defense". This overall it is supposed allows us to tailor our mitigation to those moments we need it most, choosing when to have that additional 50% dodge. The kind of stats needed to achieve this build are a combination of hit, expertise, critical strike, and haste. Another benefit to this "rps" form of mitigation is that the guardian will achieve higher dps, which can sometimes be useful for meeting tough timers.

Of course, some might also wish to mix and match the above tactics - swapping between mastery/dodge and agility/critical strike trinkets.

These two separate methods are why there isn't just a single "stat X, stat Y, stat P" clear cut build. And this lack of clarity is why there might be some confusion among people who are not familiar or are only just getting started with guardian tanking.

Edit: With a player just beginning as a guardian, I personally would recommend a combination of mastery and expertise/hit. This will offer you more than a minimal amount of rage to play with, and thus offer you the chance to play with those active mitigation tools like "Savage Defense". Likewise, it will offer you passive mitigation so that should you find yourself stuck without rage from moment to moment you won't get completely destroyed. This method however may only be effective for LFR quality bosses.

On a personal note, I run the RPS mitigation build, and have now cleared every boss on heroic on the current tier using it (except Vizier HC I think).

i think its also importent to state that the RPS setup lets you tank magical dmg fights, and bleed effect fight such as stone gaurd and elgelon and tsaulong
the dodge / armor setup will only have effect on fight with high melee attacks